I am one of the individuals that did this. My goal was to find out what shot the best at 100 yards and past.
All of the bullets/powder combinations I tried over that particular spring and summer, shot really tight patterns at 50 yards and in. I wanted to take my ability of using peep sights out of the equation at 100 yards and beyond. I shot several different loads one summer with a scope and found a pretty good bullet / powder combination that was really consistant out to 200 yards. I then took my scope off and started from scratch again and tried to recreate the patterns at 100 yards with the peep sights. My patterns were not as tight at 100 yards with peep sights as they were with the scope, but with the new load my patterns were tighter than when I originally started with peep sights.
This is not normal for most folks that hunt with the muzzleloader, but I have played with multiple bullets / powder combinations, spending hundreds of pesos on bullets and powders over the years. I wanted to improve my data with fewer numbers of shots and less dollars by taking my operation of peep sights out of the equation. Plus if i ever do hunt one of these states that allows scoped muzzleloaders, i now have the rings for it. The rings were cheaper for me than the extra 100 shots I would have taken that summer.
I also wanted to know how well I could shoot with the muzzleloader with a scope. I think I had it down to about less than 6 inch groups at 225 for a 4 shot group, if I recall correctly. This was a couple of seasons ago, and I don't have my data in front of me. I think I can do better with going from 275 grain bullet to 325 grain bullet purely due to the length and balistic co-efficient, but I haven't tried that combination yet.